This invention relates to an open-cycle compression-intercooled gas generator operating at high cycle pressure ratios of 35 to 65 atmospheres. The said gas generator exhausts hot gas at relatively high velocity and pressure to a diffuser where a majority of the velocity pressure is converted to static pressure. The converted gas then is reheated in a reheat combustor before being expanded through a power turbine to produce mechanical work, generally considered to be electrical power.
The air is intercooled at a particular and specific pressure to minimize the overall combined cycle efficiency degradation when said gas generator, diffuser, reheat combustor and power turbine are operating in conjunction with a heat recovery boiler and a steam or vapor turbine. The boiler can evaporate water, ammonia, freon or some other liquid or a mixture thereof to form superheated vapor for expansion through a vapor turbine such as a steam turbine. A combined cycle is accordingly formed whereby the overall combined cycle efficiency can range from 50 to 65% (LHV) depending upon the gas generator and power turbine inlet temperatures and the bottoming steam or vapor cycle selected.
An integral single-bodied gas generator with a coaxial shafting arrangement for driving the low pressure and high-pressure compressor sections with intercooling connections is made possible whereby gas generators such as the GE LM5000, RR RB211, P&WA JT9 and subsequent third-generation gas generators expected to be developed from the NASA E.sup.3 (Energy Efficient Engine) aircraft gas turbine program can be applied through proper modifications. The advantage of quick installation and removal of aeroderivative gas generators can be retained.
A pressure retaining casing arrangement around the high pressure portion of said gas generator, that is the high pressure compressor, the combustor and the turbine section, is provided to contain the higher than normal pressure of said gas generator. The GE LM5000 operates at a cycle pressure ratio of about 30 and the new engines to be derived from the E.sup.3 program will operate at pressure ratios of about 38 atmospheres. The gas generator of this invention would operate at pressures of 35 to 65 atmospheres, but preferably at about 50. The pressure-retaining casing makes it possible to adapt light-weight aeroderivative gas generators with light-weight casings for the higher pressure levels of this invention without exceeding safe blow-out casing pressures.
The reheat-gas-turbine combined cycle is being seriously considered as a way to obtain a higher combined-cycle efficiency than otherwise obtainable from the simple-cycle gas turbine. The Japanese Government is well along in testing its 122 MW compression-intercooled reheat gas turbine and field-test results will be made available in mid-1984.
The Japanese reheat-gas-turbine configuration incorporates compression intercooling to accomplish a projected 55 percent (LHV) combined-cycle efficiency. Intercooling is done at about a 4.85 ratio by direct-contact condensate spray water. The intercooling of my invention takes place at a much lower and specific pressure with an optimum ratio range of about 2.0 to 2.5 and uses condensate and cooling-tower, lake, river or sea water as the coolant in a primary closed loop and an open or closed secondary loop. Ammonia or a mixture of ammonia and water can also be used as the intercooler coolant where a dry-type atmospheric cooling system is employed. Direct-contact water-spray cooling can also be used.
Studies of the non-intercooled reheat-gas-turbine combined cycle show that such an arrangement will produce the highest combined-cycle efficiency for any given gas generator and reheat-turbine inlet temperatures. However, the non-intercooled gas generator is limited to about 40 atmospheres primarily due to the high compressor discharge temperatures associated with the high compressor pressure. My invention makes it possible to exceed the 40 atmospheres and provide a lower compressor-discharge temperature needed for said gas generator combustor-liner cooling and NO.sub.x control.
Industrializing the E.sup.3 engine gas generators, considered to be the third generation of aircraft engines, is inevitable based on past history, and adapting them for intercooling can be accomplished using the basic engine designs coming from the E.sup.3 program and applying the process principles and design features of this invention. Adaptation of the E.sup.3 engine such as the Pratt and Whitney Aircarft 2037 and 4000 series engines as well as similar engines by General Electric and Rolls Royce being readied for aircraft service can be applied.
In U.S. Pat. No. 4,272,953 applicant has disclosed that second generation, high-cycle pressure ratio, high-firing temperature gas generators can be used in the reheat gas turbine/steam turbine combined cycle to yield increased efficiency and output heretofore unexpected from reheat-gas-turbine combined cycles. A novel reheat gas turbine without intercooling combined with a steam turbine is further disclosed in applicant's pending application, U.S. Ser. No. 224,496 filed Jan. 13, 1981. In this pending application the reheat gas turbine comprises a juxtaposed and axially aligned gas generator and power turbine in which gas flow through the gas generator, reheat combustor and power turbine is substantially linear throughout, but nothing is given on the compression intercooling in either disclosure.
Other U.S. patents and pending applications by the applicant, all pertaining to the reheat gas turbine and steam cooling, but not specifically to compression intercooling are as follows:
U.S. Pat. No. 4,314,442 PA1 U.S. Pat. No. 4,384,452 PA1 U.S. Ser. No. 416,171 PA1 U.S. Ser. No. 416,172 PA1 U.S. Ser. No. 416,173 PA1 U.S. Ser. No. 416,275 PA1 U.S. Ser. No. 486,334 PA1 U.S. Ser. No. 486,336 PA1 U.S. Ser. No. 486,495.
Intercooling has been used for many years with compression of air and other gaseous fluids to reduce the power required for compression. Also simple-cycle and reheat-cycle gas turbines have incorporated air compression intercooling to reduce compression work and consequently to increase the gas turbine output, particularly for regenerative-cycle gas turbines not involving a combined cycle. However, in such cases the emphasis has been on maximizing output and gas turbine efficiency and not to optimize combined cycle efficiency. As will be shown, the compression intercooling in past gas turbines takes place at a much higher pressure ratio than the analytical discovery of my invention indicates as being optimum for combined cycle efficiency. The Japanese Government is developing an intercooled reheat gas turbine for combined cycle service, but water-spray intercooling is employed at a much higher intercooled compression ratio than that of my invention.
A coaxial shafting arrangement is contemplated whereby the initial (low pressure) compressor is driven by a turbine by means of a shaft running through the high-pressure compressor, the high-pressure turbine and the interconnecting shaft. Coaxial drives are highly developed for high-bypass fan jets and indeed gas generators such as General Electric's LM5000, General Motors 570K and Rolls-Royce's RB-211. However, no intercooling is used or even remotely suggested. It is the increase in the low-pressure compressor diameter made possible by the intercooling that permits adequate physical space for the air to be exited and readmitted efficiently with a minimum of pressure loss.
Further, when such type generators as the LM5000 or 570K or future third-generation aeroderivatives are modified for intercooling, the high-pressure sections (high-pressure compressor housing, combustor housing and high-pressure turbine housing) are subjected to much higher internal pressures. The cycle pressure ratios will increase from 18, 30 or 38, as the case may be, to some 35 to 65 due to the supercharging. In order for such gas generators to be adapted for compression intercooling and the higher cycle pressure ratios suitable for the reheat gas turbine and the combined cycle something has to be done about the added pressure to prevent casing rupture and/or distortion due to the higher internal pressure. This invention deals with the added pressure and the prevention of distortion and blow-out by incorporating a special and unique cylindrical pressure chamber with thermal expansion joints around the gas generator. Air is presently being used to cool the advanced aero gas-turbine casings to control rotating blade-tip clearance. This invention uses steam inside the pressure chamber not only to provide casing cooling but to also provide cooling for the internal gas-generator parts.